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Biological Applications Of Quantum Dots - Patent 6855551

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This invention relates to a composition comprising fluorescent semiconductor nanocrystals associated with compounds for use in biological applications.BACKGROUND OF THE INVENTIONTraditional methods for detecting biological compounds in vivo and in vitro rely on the use of radioactive markers. For example, these methods commonly use radiolabeled probes such as nucleic acids labeled with .sup.32 P or .sup.35 S andproteins labeled with .sup.35 S or .sup.125 I to detect biological molecules. These labels are effective because of the high degree of sensitivity for the detection of radioactivity. However, many basic difficulties exist with the use of radioisotopes. Such problems include the need for specially trained personnel, general safety issues when working with radioactivity, inherently short half-lives with many commonly used isotopes, and disposal problems due to full landfills and governmental regulations. As a result, current efforts have shifted to utilizing non-radioactive methods of detecting biological compounds. These methods often consist of the use of fluorescent molecules as tags (e.g. fluorescein, ethidium, methyl coumarin, rhodamine, and Texasred), or the use of chemiluminescence as a method of detection. Presently however, problems still exist when using these fluorescent and chemiluminescent markers. These problems include photobleaching, spectral separation, low fluorescence intensity,short half-lives, broad spectral linewidths, and non-gaussian asymmetric emission spectra having long tails.Fluorescence is the emission of light resulting from the absorption of radiation at one wavelength (excitation) followed by nearly immediate reradiation usually at a different wavelength (emission). Fluorescent dyes are frequently used as tagsin biological systems. For example, compounds such as ethidium bromide, propidium iodide, Hoechst dyes, and DAPI (4',6-diamindino-2-phenylindole) interact with DNA and fluoresce to visualize DNA. Other biological co

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